Method and apparatus for detecting anatomical elements

ABSTRACT

A method, apparatus and computer program product are hereby provided to detect anatomical elements in a medical image. In this regard, the method, apparatus, and computer program product may receive a test image and generate a classified image by applying an image classifier to the test image. The image classifier may include at least one decision tree for evaluating at least one pixel value of the test image and the classified image may include a plurality of pixel values. Each pixel value may be associated with a probability that an anatomical element is located at the pixel location. The method, apparatus, and computer program product may also evaluate the classified image using an anatomical model to detect at least one anatomical element within the classified image.

TECHNOLOGICAL FIELD

An example embodiment of the present invention relates generally tomedical imaging applications, and, more particularly, to a method andapparatus for detecting anatomical elements within a medical image.

BACKGROUND

As medical technology has advanced, it is increasingly common forpractitioners to interpret data received from one or more medicalimaging devices. Different types of imaging devices (e.g., x-ray images,computed tomography scans, magnetic resonance imaging (“MRI”) scans)produce different types of output images, and medical practitionersreceive extensive training in performing diagnoses based on theseimages. However, analysis of these images may involve various timeconsuming processes, such as manual labeling of elements within animage. For example, a practitioner might spend a significant amount oftime manually applying labels to vertebrae in a spinal x-ray or MRI scanin order to report a spinal problem. These manual processes may delaypatient results and reduce the availability of the practitioner toperform other tasks. User errors during these processes may result inincorrect or delayed reports. Through applied effort, ingenuity, andinnovation, applicant has solved many of these identified problems bydeveloping a solution that is embodied by the present invention, whichis described in detail below.

BRIEF SUMMARY

Accordingly, a method, apparatus and computer program product aretherefore provided according to an example embodiment of the presentinvention in order to provide improved detection of anatomical elementswithin medical images. In this regard, the method, apparatus, andcomputer program product of an example embodiment may receive a set oftraining images. The set of training images may be analyzed to generatea classifier. The set of training images may also be used to generate ananatomical model. A test image may be processed using the classifier todetermine a set of probabilities associated with locations of anatomicalfeatures. The processed test image may then be analyzed using theanatomical model to determine the locations of one or more anatomicalfeatures within the image. Embodiments may apply labels to theseanatomical features within the test image to assist a practitioner ininterpreting the test image.

Embodiments may include a method for detecting anatomical elements. Themethod may include receiving a test image, generating a classified imageby applying an image classifier to the test image. The image classifiermay include at least one decision tree for evaluating at least one pixelvalue of the test image and the classified image comprising a pluralityof pixel values. Each pixel value may be associated with a probabilitythat an associated pixel is related to an anatomical element. The methodmay also include evaluating, using a processor, the classified imageusing an anatomical model to detect at least one anatomical elementwithin the classified image. The method may also include labeling thedetected at least one anatomical element within the test image inresponse to detecting the at least one anatomical element within theclassified image. A location of the anatomical element within the testimage may correspond to a location in which the anatomical element wasdetected within the classified image. The method may also includegenerating the image classifier by receiving a set of training images.The set of training images may include at least one target image and atleast one source image. The method may also include determining at leastone image feature, transforming the at least one source image using theat least one image feature to generate at least one feature image,generating at least one decision tree corresponding to the at least oneimage feature using at least the at least one feature image and the atleast one target image, and using the generated at least one decisiontree as the image classifier. The method may include generating aplurality of decision trees, each of the decision trees corresponding toa set of image features, evaluating the plurality of decision trees todetermine an accuracy value for each decision tree, and selecting atleast one of the plurality of decision trees with the highest accuracyvalue as the image classifier. The at least one image feature may be aHaar-like feature. The at least one decision tree may be generated by aprocess including determining a set of pixel values associated with aparticular node of the decision tree, determining a feature that resultsin a minimum variance in target pixel values associated with the set ofpixel values, and assigning the feature that results in a minimumvariance in target pixel values as a decision feature for the particularnode of the tree. In some embodiments, the method may includedetermining a threshold feature value associated with the feature thatresults in the minimum variance. The threshold feature value may resultin a split in the set of pixel values when applied to the set of pixelvalues. The method may also include assigning the threshold featurevalue to the particular node of the decision tree. The method mayinclude generating the anatomical model by evaluating a set ofanatomical data. The anatomical model may define at least one of a sizeof an anatomical element, a shape of an anatomical element, or an offsetbetween two or more anatomical elements. In some embodiments, theanatomical elements are spinal vertebrae, and the anatomical modeldefines an offset between adjacent vertebrae.

Embodiments may also include an apparatus including processingcircuitry. The apparatus may be configured to receive a test image, andgenerate a classified image by applying an image classifier to the testimage. The image classifier may include at least one decision tree forevaluating at least one pixel value of the test image. The classifiedimage may include a plurality of pixel values. Each pixel value may beassociated with a probability that an associated pixel is related to ananatomical element. The apparatus may also be configured to evaluate theclassified image using an anatomical model to detect at least oneanatomical element within the classified image. The apparatus may befurther configured to label the detected at least one anatomical elementwithin the test image in response to detecting the at least oneanatomical element within the classified image. A location of theanatomical element within the test image may correspond to a location inwhich the anatomical element was detected within the classified image.The apparatus may be further configured to receive a set of trainingimages, the set of training images comprising at least one target imageand at least one source image, to determine at least one image feature,to transform the at least one source image using the at least one imagefeature to generate at least one feature image, to generate at least onedecision tree corresponding to the at least one image feature using atleast the at least one feature image and the at least one target image,and to use the generated at least one decision tree as the imageclassifier. The apparatus may be further configured to generate aplurality of decision trees, each of the decision trees corresponding toa set of image features, to evaluate the plurality of decision trees todetermine an accuracy value for each decision tree, and to select atleast one of the plurality of decision trees with the highest accuracyvalue as the image classifier. The apparatus may also be configured todetermine a set of pixel values associated with a particular node of thedecision tree, to determine a feature that results in a minimum variancein target pixel values associated with the set of pixel values, and toassign the feature that results in a minimum variance in target pixelvalues as a decision feature for the particular node of the tree. Insome embodiments, the apparatus may be configured to determine athreshold feature value associated with the feature that results in theminimum variance. The threshold feature value may result in a split inthe set of pixel values when applied to the set of pixel value. Theapparatus may also be configured to assign the threshold feature valueto the particular node of the decision tree. In some embodiments, theanatomical elements are spinal vertebrae, and the anatomical model maydefine an offset between adjacent vertebrae.

Embodiments may also provide a computer program product comprising atleast one non-transitory computer-readable storage medium bearingcomputer program instructions embodied therein for use with a computer.The computer program instructions may include program instructionsconfigured to receive a test image, to generate a classified image byapplying an image classifier to the test image. The image classifier mayinclude at least one decision tree for evaluating at least one pixelvalue of the test image and the classified image comprising a pluralityof pixel values. Each pixel value may be associated with a probabilitythat an associated pixel is related to an anatomical element. Theprogram instructions may also be configured to evaluate the classifiedimage using an anatomical model to detect at least one anatomicalelement within the classified image.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described certain embodiments of the invention in generalterms, reference will now be made to the accompanying drawings, whichare not necessarily drawn to scale, and wherein:

FIG. 1 is a block diagram of an apparatus that may be specificallyconfigured in accordance with example embodiments of the presentinvention;

FIG. 2 is a block diagram of a data flow for generating a classifier andan anatomical model from a set of training images in accordance withexample embodiments of the present invention;

FIG. 3 is a block diagram of an overview of an example process forlabeling a medical image in accordance with example embodiments of thepresent invention;

FIG. 4 is a flow diagram of an example method for labeling a medicalimage in accordance with example embodiments of the present invention;

FIG. 5 is a flow diagram of an example method for determining an imageclassifier from a set of training images in accordance with exampleembodiments of the present invention;

FIG. 6 is an illustration of an example set of two dimensional Haar-likefeatures used for determining an image pixel classifier in accordancewith example embodiments of the present invention;

FIG. 7 is an illustration of image samples from a set of training imagesin accordance with example embodiments of the present invention;

FIG. 8 is a flow diagram of an example method for generating aclassification tree in accordance with example embodiments of thepresent invention;

FIG. 9 is a flow diagram of an example method for selecting features fornodes of a classification tree in accordance with example embodiments ofthe present invention;

FIG. 10 is a flow diagram of an example method for selecting one or moreoptimal classification trees for use in an image classifier inaccordance with example embodiments of the present invention;

FIG. 11 is a flow diagram of an example method for generating aclassified image using an image classifier in accordance with exampleembodiments of the present invention; and

FIG. 12 is a flow diagram of an example method for generating ananatomical model in accordance with example embodiments of the presentinvention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Overview

A method, apparatus and computer program product are provided inaccordance with an example embodiment of the present invention in orderto label medical images. In this regard, a method, apparatus andcomputer program product of an example embodiment may utilize an imageclassifier to generate a classified image, where the classified imagecomprises pixel values representing the probability of the particularpixel belonging to an anatomical element within a test image. Theclassified image may be analyzed according to an anatomical model todetermine a predicted location of the anatomical elements, and thepredicted locations may be used to label anatomical elements within thetest image.

As used herein, the term “anatomical elements” should be understood torefer to any patient data that can be derived from review of a medicalimage. For example, anatomical elements should be understood to include,without limitation, organs, nerves, veins, arteries, or any otherpatient anatomy or function that may be captured using a medical imagingdevice. It should also be appreciated that the term “anatomical element”may also include elements that, while not part of the patient's body,are still related to patient anatomy and which may be visualized in amedical image. For example, “anatomical elements” should also beunderstood to include surgical instruments, implants, parasites,injuries, and various other elements that can be discerned and/ordiagnosed using medical imaging techniques. In addition, “anatomicalelements” should also be understood to represent functional regions,regions of activation, regions of high uptake of X-ray, or the like.

Example Apparatus

FIG. 1 illustrates a block diagram of an apparatus 102 in accordancewith some example embodiments. The apparatus 102 may be any computingdevice capable of receiving a test image and processing the test imageto detect one or more anatomical elements. In some particularembodiments, the apparatus 102 may be configured to perform or otherwiseassist with medical diagnostic and/or imaging operations. For example,the apparatus 102 may be implemented on a computing device that may beconfigured to access and display images stored in a Digital Imaging andCommunications in Medicine (DICOM) format. Accordingly, it will beappreciated that the apparatus 102 may comprise an apparatus configuredto implement and/or otherwise support implementation of various exampleembodiments described herein.

It should be noted that the components, devices or elements illustratedin and described with respect to FIG. 1 below may not be mandatory andthus some may be omitted in certain embodiments. Additionally, someembodiments may include further or different components, devices orelements beyond those illustrated in and described with respect to FIG.1.

The apparatus 102 may include or otherwise be in communication withprocessing circuitry 110 that is configurable to perform actions inaccordance with one or more example embodiments disclosed herein. Inthis regard, the processing circuitry 110 may be configured to performand/or control performance of one or more functionalities of theapparatus 102 (e.g., functionalities of a computing device on which theapparatus 102 may be implemented) in accordance with various exampleembodiments, and thus may provide means for performing functionalitiesof the apparatus 102 (e.g., functionalities of a computing device onwhich the apparatus 102 may be implemented) in accordance with variousexample embodiments. The processing circuitry 110 may be configured toperform data processing, application execution and/or other processingand management services according to one or more example embodiments. Insome embodiments, the apparatus 102 or a portion(s) or component(s)thereof, such as the processing circuitry 110, may be embodied as orcomprise a chip or chip set. In other words, the apparatus 102 or theprocessing circuitry 110 may comprise one or more physical packages(e.g., chips) including materials, components and/or wires on astructural assembly (e.g., a baseboard). The apparatus 102 or theprocessing circuitry 110 may therefore, in some cases, be configured toimplement an embodiment of the invention on a single chip or as a single“system on a chip.” As such, in some cases, a chip or chipset mayconstitute means for performing one or more operations for providing thefunctionalities described herein.

In some example embodiments, the processing circuitry 110 may include aprocessor 112 and, in some embodiments, such as that illustrated in FIG.1, may further include memory 114. The processing circuitry 110 may bein communication with or otherwise control a user interface 116 and/or acommunication interface 118. As such, the processing circuitry 110 maybe embodied as a circuit chip (e.g., an integrated circuit chip)configured (e.g., with hardware, software or a combination of hardwareand software) to perform operations described herein.

The processor 112 may be embodied in a number of different ways. Forexample, the processor 112 may be embodied as various processing meanssuch as one or more of a microprocessor or other processing element, acoprocessor, a controller or various other computing or processingdevices including integrated circuits such as, for example, an ASIC(application specific integrated circuit), an FPGA (field programmablegate array), or the like. Although illustrated as a single processor, itwill be appreciated that the processor 112 may comprise a plurality ofprocessors. The plurality of processors may be in operativecommunication with each other and may be collectively configured toperform one or more functionalities of the apparatus 102 as describedherein. The plurality of processors may be embodied on a singlecomputing device or distributed across a plurality of computing devicescollectively configured to function as the apparatus 102. In someexample embodiments, the processor 112 may be configured to executeinstructions stored in the memory 114 or otherwise accessible to theprocessor 112. As such, whether configured by hardware or by acombination of hardware and software, the processor 112 may represent anentity (e.g., physically embodied in circuitry—in the form of processingcircuitry 110) capable of performing operations according to embodimentsof the present invention while configured accordingly. Thus, forexample, when the processor 112 is embodied as an ASIC, FPGA or thelike, the processor 112 may be specifically configured hardware forconducting the operations described herein. Alternatively, as anotherexample, when the processor 112 is embodied as an executor of softwareinstructions, the instructions may specifically configure the processor112 to perform one or more operations described herein.

In some example embodiments, the memory 114 may include one or morenon-transitory memory devices such as, for example, volatile and/ornon-volatile memory that may be either fixed or removable. In thisregard, the memory 114 may comprise a non-transitory computer-readablestorage medium. It will be appreciated that while the memory 114 isillustrated as a single memory, the memory 114 may comprise a pluralityof memories. The plurality of memories may be embodied on a singlecomputing device or may be distributed across a plurality of computingdevices collectively configured to function as the apparatus 102. Thememory 114 may be configured to store information, data, applications,instructions and/or the like for enabling the apparatus 102 to carry outvarious functions in accordance with one or more example embodiments.For example, the memory 114 may be configured to buffer input data forprocessing by the processor 112. Additionally or alternatively, thememory 114 may be configured to store instructions for execution by theprocessor 112. As yet another alternative, the memory 114 may includeone or more databases that may store a variety of files, contents ordata sets. Among the contents of the memory 114, applications may bestored for execution by the processor 112 in order to carry out thefunctionality associated with each respective application. In somecases, the memory 114 may be in communication with one or more of theprocessor 112, user interface 116, or communication interface 118 via abus or buses for passing information among components of the apparatus102.

The user interface 116 may be in communication with the processingcircuitry 110 to receive an indication of a user input at the userinterface 116 and/or to provide an audible, visual, mechanical or otheroutput to the user. As such, the user interface 116 may include, forexample, a keyboard, a mouse, a joystick, a display, a touch screendisplay, a microphone, a speaker, a Light Emitting Diode (LED), alighting device, an electronic sensor for capturing human bodymovements, and/or other input/output mechanisms. In embodiments in whichthe apparatus 102 is implemented on a server, aspects of the userinterface 116 may be limited, or the user interface 116 may even beeliminated. For example, the apparatus 102 may act as a server or hostdevice, with a user interface provided by a client application.

The communication interface 118 may include one or more interfacemechanisms for enabling communication with other devices and/ornetworks. In some cases, the communication interface 118 may be anymeans such as a device or circuitry embodied in either hardware, or acombination of hardware and software that is configured to receiveand/or transmit data from/to a network and/or any other device or modulein communication with the processing circuitry 110. By way of example,the communication interface 118 may be configured to enable theapparatus 102 to communicate with another computing device via awireless network, such as a wireless local area network (WLAN), cellularnetwork, and/or the like. Additionally or alternatively, thecommunication interface 118 may be configured to enable the apparatus102 to communicate with another computing device via a wireline network.For example, the apparatus 102 may obtain an image of a patient, andlabel the image with the location of one or more anatomical elements. Insome example embodiments, the communication interface 118 may beconfigured to enable communication between the apparatus 102 and one ormore further computing devices via the Internet. Accordingly, thecommunication interface 118 may, for example, include an antenna (ormultiple antennas) and supporting hardware and/or software for enablingcommunications with a wireless communication network (e.g., a wirelesslocal area network, cellular network, and/or the like) and/or acommunication modem or other hardware/software for supportingcommunication via cable, digital subscriber line (DSL), universal serialbus (USB), Ethernet or other methods.

Having now described an apparatus configured to implement and/or supportimplementation of various example embodiments, features of severalexample embodiments will now be described. It will be appreciated thatthe following features are non-limiting examples of features provided bysome example embodiments. Further, it will be appreciated thatembodiments are contemplated within the scope of disclosure thatimplement various subsets or combinations of the features furtherdescribed herein. Accordingly, it will be appreciated that some exampleembodiments may omit one or more of the following features and/orimplement variations of one or more of the following features.

Example Training Set Data Flow

FIG. 2 is a block diagram of a process flow 200 for generating an imageclassifier and an anatomical model in accordance with exampleembodiments of the present invention. The process flow 200 may include atraining module 202 that receives a set of training images 204. The setof training images 204 may include a plurality of images, including oneor more target images 206 and one or more source images 208. The targetimages 206 represent a mapping of the location of particular anatomicalelements to be detected by a generated image classifier. For example, atarget image 206 might include data specifying the location of vertebraein a spinal image. In the present example, the pixels of the targetimage 206 only display the locations of vertebrae. Each of the targetimages 206 may be associated with a particular source image 208,representing an image from which the corresponding target image 206 wasderived. For example, a target image 206 and source image 208 pair mightinclude a raw MRI scan of a patient spine as the source image 208 and animage containing only the patient's vertebrae as the target image 206.The source image 208 and the target image 206 may be linked together,such that pixel locations within the source image 208 correspond topixel locations in the target image 206. In some embodiments, the set oftraining images may include images from multiple viewing angles of thesame medical study, allowing a three dimensional analysis to beperformed. The set of training images 204 may be used by the trainingmodule 202 to generate an image classifier 210. The image classifier 210may be generated by applying one or more feature detectors to the sourceimage to generate a set of feature images, and processing the featureimages to construct a plurality of classification trees. Theseclassification trees may be analyzed to determine which classificationtrees are optimal for classifying the particular set of training images,and the optimal classification trees may be used as image classifiers ina labeling operation (e.g., voting processes that provide aprobabilistic class for the pixels) performed on a test image. Exampleembodiments for generating and implementing such a classifier aredescribed further below with respect to FIGS. 3-12.

The set of training images 204 may also be used by the training module202 to generate an anatomical model 212. The anatomical model 212 mayinclude a set of data used to evaluate the locations of anatomicalelements in relation to one another. For example, a given set oftraining data may correspond to medical images of a patient's spine. Theanatomical model may examine the known locations of patient vertebrae asidentified within the set of training images to generate an anatomicalmodel for the distance between the vertebrae depicted in the set oftraining images 204. As such, the anatomical model may be used topredict the distance between vertebrae of a sample image. Examplemethods for utilizing and generating such a model are described furtherbelow with respect to FIGS. 3-4 and 12.

Example Labeling Data Flow

Turning now to FIG. 3, an example data flow 300 for labeling anatomicalelements within a medical image is depicted. The data flow 300 includesa training phase 302, which includes generating one or more imageclassifiers and an anatomical model. The image classifier is generatedand utilized in a feature detection phase 304, and the anatomical modelis generated and utilized in a pictorial phase 306. It should be readilyappreciated that, while the training phase 302 is shown as overlappingwith portions of the feature detection phase 304 and the pictorial phase306, the training phase 302 could be decoupled from the use of the imageclassifier and anatomical model to label medical images. For example,the training phase 302 could be performed as part of a calibration orconfiguration step at a factory or laboratory, and a set ofpre-generated image classifiers and anatomical models could be providedalong with sale of a product or device used for labeling of anatomicalimages. As a specific example, the image classifiers and anatomicalmodels could be included as one or more models or databases in the saleof an electronic medical imaging device (e.g., an MRI machine, a CTscanner, or an image analysis software program). The feature detectionphase 304 begins during the training phase 302 at action 308, where aset of features 310 are determined. The set of features 310 may berandomly determined and used for detecting objects within a given imageaccording to various image recognition techniques. For example, thefeatures 310 may be “Haar-like” features, which include adjacentrectangular regions at a specific location in a detection window.Examples of these features are described further below with respect toFIG. 6. The feature detection phase 304 may receive certain options 310to configure the feature determination process. For example, the options310 may include user options that define particular Haar-like features,sets of training data (e.g., selection of a set of training dataassociated with a particular anatomical feature to be detected or amedical image type to be analyzed) or constraints placed upon the set oftraining data.

The determined features 310 may be provided to a classifier trainer 316.The classifier trainer 316 may apply the determined features 310 to aset of training data 314, such as described above with respect to FIG.2. Applying the features to the set of training data 314 may includeconvolving a feature with a given source image selected from the set oftraining data to generate a feature image. The source image may beconvolved with each of the features to generate a feature vector imageassociated with the source image. These feature vector images may beused in concert with a target image to generate one or more imageclassifiers 320 from the set of training data. The process of generatingthe image classifier(s) 320 may include receiving one or more options318 to modify the image classifier generation process. For example, theoptions 318 may indicate which training images should be used, how largethe set of training images should be, how large the set of determinedfeatures should be, or the like. The options 318 may specify, forexample, which anatomy should be treated similarly with respect toparticular features, and the depth and number of decision trees utilizedduring the analysis. In other examples, the options 318 may include aratio of negative vs. positive targets to sample in training phase(e.g., rather than a completely random sample the analysis may sampleall of these pixels and then only a select few ‘negative’ target pixelswhen selecting pixels to sample for construction of decision trees), thesize of Gaussian used when converting from an anatomical target position(e.g., a labeled vertebrae position) to a target image. Instead ofcreating a target image by simply putting one 100% probability point atthe position of the vertebrae, embodiments may instead mark a fuzzysphere (created by a Gaussian) around that point. Example embodiments ofmethods for generating the image classifier 320 are described furtherbelow with respect to FIGS. 5-10.

The set of training data 314 may also be employed to generate ananatomical model 326 using a pictorial image evaluation technique duringthe pictorial phase 306. At operation 322, the set of training data maybe analyzed to identify the location of particular anatomical elements.A target image that indicates the location of anatomical elements may beevaluated to determine a relationship between the locations of theanatomical elements. For example, the set of training data may includeseveral images of patient spines with labeled vertebrae, and a model forthe vertebrae location may be determined by identifying the positionoffsets (e.g., the distance between the centers of each vertebra)depicted in the set of training data. An example embodiment forgenerating an anatomical model is described further below with respectto FIG. 12. The anatomical model generation process may be modified byone or more options 324. For example, the options may specify the typeof anatomical data to be modeled, which variables are to be used in theanatomical model, which training images should be used to generate themodel, or the like. The options 324 may specify, for example,definitions for the anatomical model, such as which anatomical elementpositions are linked to and influenced by which other anatomicalelements. In some embodiments, training images may be selected by theoptions 324 as well.

At operation 328, the image classifier 320 may be applied to a testimage 330. Applying the classifier may be used to determine theprobability that particular pixels within the test image 330 areassociated with particular anatomical elements. The output of the imageclassifier 320 as applied to the test image 330 may include a classifiedimage 334 where the likelihood of a particular anatomical element beinglocated at a particular pixel is represented by a contrast, color,intensity, hue, or other value associated with the pixel, or aneighborhood of the pixel. This classified image 334 may be provided tothe pictorial phase 306 for use with the anatomical model 336 todetermine the location of one or more anatomical elements. The imageclassification process 328 may receive and be configured by one or moreoptions 332. For example, the options may include various configurableparameters for modifying an output probability image, such as forsmoothing the image to improve spatial regularity and reducing potentialfalse positive results. These options may indicate, for example, thedegree of this smoothing process.

At operation 336, the anatomical model is applied to the classifiedimage using a pictorial algorithm. The pictorial algorithm may includethe anatomical model to identify anatomical structures within theclassified image. For example, an anatomical model that identifies theoffsets between spinal vertebrae may be used to detect the shape andlocation of spinal structures based on the probability distributionswithin the classified image. In some embodiments the pictorial algorithmmay be configured by certain options 338, such as but not limited toselection of a particular anatomical model to be applied. The output ofthe pictorial algorithm 336 may be a set of labels applied to the testimage, indicating the determined location of the anatomical elements orprobabilities of anatomical elements belonging in those locations. Forexample, the pictorial algorithm as described above may label the centerof each vertebra in a medical image depicting a patient's spinal column.

Example Flow Diagram for Labeling a Medical Image

Turning now to FIG. 4, an example embodiment of the method 400 forlabeling a medical image is described. As described above with respectto FIGS. 2 and 3, the method 400 may serve to first generate an imageclassifier and an anatomical model from a set of training data, and thenapply the image classifier and the anatomical model to a test image todetect and label anatomical features depicted in the test image. In someembodiments, the method 400 may be performed by a processor, such as theprocessor 112 or an apparatus, such as the apparatus 102.

At action 402, a set of training images are received. As described withrespect to FIG. 2, the training images may include a set of targetimages and a set of source images. The target images may include a setof locations or location probabilities of one or more anatomicalelements and the source images may correspond to medical images fromwhich the target images were derived.

At action 404, an image classifier may be generated using the set oftraining images. For example, one or more features may be applied toeach of the source images to generate a set of feature images, and thefeature images may be analyzed to determine whether each feature imageprovides an improved representation of the locations of the anatomicalelements by comparing the results of the feature image to the resultsfrom other feature images to identify the feature images that bestdiscriminate between parts of the input image. Example methods forgenerating an image classifier are described in further detail withrespect to FIGS. 5-10, below.

At action 406, an anatomy model is generated. The anatomy model may begenerated using a set of known locations of anatomical elements. Theanatomy model may include a set of location offsets for anatomicalelements. For example, the anatomy model may model the size, shape,and/or structure of a set of spinal vertebrae by identifying a distancebetween certain adjacent vertebrae. The anatomy model may be generatedby fitting a curve or function (e.g. a Gaussian) to the set of knownlocations of anatomy elements.

The set of training images may include one or more images that indicateknown locations of anatomical elements for use in generating the anatomymodel. Additionally or alternatively, the set of known locations ofanatomical elements may be provided in another manner other than as partof the set of training images. For example, a matrix or data table ofanatomical elements may be used to generate the anatomy model, such thatthe anatomy model may be generated without the use of any image analysistechniques. An example of a method for generating the anatomy model isdescribed further below with respect to FIG. 12.

At action 408, a test image (e.g., an image where the locations ofanatomical elements are unknown) may be received. The test image may bereceived directly from an imaging device, via a network connection, as amanual file selection by a user, as part of an electronic communication(e.g., an e-mail), or the like. In some embodiments, the test image maybe provided in a certain format (e.g., DICOM), or according to certainother parameters (e.g., certain brightness or contrast settings, acertain viewing angle relative to a patient, or the like).

At action 410, the test image may be classified using the imageclassifier generated at action 404. The classifier may take the testimage as an input and assign each pixel of the test image a probabilityof being the location of an anatomical element. An example of a methodfor classifying a test image is described further below with respect toFIG. 11. The output of the classifier may be a classified image, whereeach pixel of the classified image is associated with a value (e.g.,contrast, hue, brightness) representing the likelihood that theparticular pixel is the location of an anatomical element (e.g., thedarker the pixel, the more likely that pixel is related to an anatomicalelement).

At action 412, the locations of anatomical elements are derived based onthe application of the anatomy model to the classified image. Anatomicalelements may be identified by determining a best fit between pixelsidentified as likely to be related to anatomical elements and thepositioning of anatomical elements according to an anatomical model. Forexample, the anatomy model may define a series of offsets or locationsthat, relative to one another, define a typical structure for a set ofanatomical elements (e.g., an expected location of a next spinalvertebra based on the estimated location of a first spinal vertebra).The anatomy model may be applied to various possible anatomical elementsidentified within the classified image to identify a set of probableanatomical elements that maximize the probabilities within theclassified image while minimizing the error of location calculationsderived from the anatomy model.

Various optimization methods may be employed to derive the locations ofanatomical elements from the anatomy model and the classified images.For example, in some embodiments, dynamic programming may be employed todetermine an optimal set of locations of the anatomical elements usingboth the anatomy model and the classified image. For example, a dynamicprogramming algorithm may examine each pixel of a classified image andapply the anatomy model to each pixel to find a set of anatomicalelement locations that minimizes the deviation from the probabilities ofthe classified image and the predicted locations based on the anatomymodel. In some embodiments, the dynamic programming algorithm mayutilize other, non-optimal evaluation methods to increase performance.For example, the algorithm may only examine pixels that have a minimumthreshold probability value as possible locations for anatomicalelements to be evaluated by the anatomy model. A set of locations withinthe image that maximize the probability distribution within theclassified image while also resulting in a minimum of error for theanatomy model may be identified as the locations of anatomical elements(e.g., the locations of the center of patient vertebra in a spinalimage).

At action 414, the set of locations may be labeled on the test imagebased on the results determined at action 412. For example, upondetermination of the locations of the patient's vertebrae, the methodmay label each vertebra with the name of the vertebra (e.g. L1, L2, L3for vertebrae of the lumbar spine, C1, C2, C3 for cervical spine, andT1, T2, T3 for thoracic spine). In this manner, the method 400 mayfunction to provide for efficient labeling of anatomical elements withinan input image.

Example Methods for Generating and Using an Image Classifier

Turning now to FIGS. 5-11, example embodiments for generating one ormore image classifiers from a set of training images and utilizing thegenerated image classifier in an anatomical element detection operationare described. These Figures illustrate the process by which a set oftraining images may be analyzed by applying Haar-like features, andgenerating a decision tree using values for the images derived from theHaar-like features. These decision trees may be evaluated for theiraccuracy in predicting the location of anatomical elements using a setof target images, and the most accurate decision trees may be selectedto be employed as an image classifier.

FIG. 5 illustrates a flow chart of a method 500 by which an imageclassifier may be generated from a set of training data. As describedabove, a set of training data may be provided including one or moretarget images (e.g., an image with the location of certain anatomicalfeatures clearly indicated), and one or more source images (e.g., imagesthat have not been processed to directly indicate the location ofanatomical features) that correspond to the target images. Generation ofa classifier may include identifying one or more features that mostclearly identify the anatomical objects within the source images, andusing those features to generate a decision tree which may subsequentlybe used as an image classifier.

At action 502, the method may generate a set of features for use in theclassifier. For example, these features may be “Haar-like” features. Theterm “Haar-like” is used to refer to the use of digital image featuresthat bear similarities to Haar wavelets, and which may include aplurality of rectangles for use in evaluating a set of image pixels. Anexample of the use of Haar-like features in image analysis techniques isdescribed in Viola and Jones, “Rapid object detection using a boostedcascade of simple features”, Computer Vision and Pattern Recognition,2001. Example Haar-like features are described further below withrespect to FIG. 6. The Haar-like features may be generated at random(e.g., by randomly selecting rectangle sizes and types) for eachtraining set. In some embodiments, a different random set of Haar-likefeatures is determined for each target image included in the trainingset.

In some other embodiments, the Haar-like features may be selectedaccording to particular criteria, or selected in advance by a user. Theselected Haar-like features may be selected based on the ability of theparticular Haar-like feature to be used to accurately detect thelocation of a particular anatomical element or element type (e.g., oneset of Haar-like features for vertebrae, another for ribs, another for acirculatory system, etc.).

At action 504, the Haar-like features are applied to a set of trainingimages to generate a set of feature images. In some embodiments, theimages may be modified or transformed prior to application of theHaar-like features. For example, the images intensity may be adjusted tochange the gradient magnitude, to square the image pixel intensities, totake the log of the image intensities, or the like. Application of theHaar-like features to the training images may include performing a setof transforms on the image based on the Haar-like feature. For example,application of the Haar-like feature to a particular pixel or set ofpixels may include considering adjacent rectangular regions defined bythe Haar-like feature and at a specific location in a detection window,summing up the pixel intensities in each region and calculating thedifference between these sums. The Haar-like features may be applied tothe training images by convolution, generating an output image for eachHaar-like feature that represents the application of the particularHaar-like feature to a particular source image. These feature images mayhave the intensity of each pixel determined by the convolution of thesource image with the Haar-like feature, such that the particularHaar-like feature used to generate the feature image may result incertain elements of the source image being emphasized (e.g., pixelintensity increased) and other elements being deemphasized (e.g., pixelintensity decreased) based on the size, shape, or location of theelements within the image.

At action 506, a decision tree is generated for the set of Haar-likefeatures. The decision tree may be generated by using a set of pixelsamples from a target image and a corresponding set of samples from thefeature images. These decision trees may include an evaluation of pixeldata at particular sample locations. An example of a method forgenerating a decision tree is described further below with respect toFIG. 8.

At action 508, the generated decision trees are compared to one anotherto identify one or more optimal decision trees. Different decision treesmay have different levels of accuracy due to the differentdiscriminating features (e.g., the Haar-like features described above)with which each tree is generated. Each tree may be generated“optimally” for a given set of features, and the comparison betweentrees may operate to select an optimal tree from the set of trees.Although each decision at each branch of a particular tree may beconsidered to be a “weak learner”, use of multiple decision pointswithin a tree may result in a good classifier. The use of multiplerandomly generated trees may result in a robust “forest” of classifiersthat generalizes well to unknown images and is less susceptible to erroras a result of noise. Different trees may “vote” for different resultsfor particular pixels, and the output of the forest of trees may be usedto derive a probability of membership in a particular class for aparticular pixel or pixels. In order to obtain results in an efficienttime frame, it may be appropriate to limit the number of decision treesemployed by selecting a subset of all generated trees for use in theclassifier. As such, action 508 may be employed to identify one or moretrees that best match a set of known target data for a given image.

In the present context, the term “optimal” decision tree may refer to adecision tree or set of decision trees that, upon analysis of a targetimage, generate a set of anatomical element location probabilities mostsimilar to the location of the anatomical elements defined within thetarget image. Evaluation of the similarity between the results of aparticular decision tree and the target image may include evaluatingboth “negative” results (e.g., where the tree indicates there is a lowprobability of an anatomical element) and “positive” results (e.g.,where the tree indicates that there is a high probability of ananatomical element). In this regard, evaluation of the decision tree mayinclude not only maximizing a detection rate (e.g., ensuring that thetree finds each anatomical element), but also minimizing a falsepositive rate (e.g., ensuring that the tree does not indicate a highprobability of an anatomical element in a location where no anatomicalelement exists).

For example, decision trees may be selected to minimize the amount oferror between a calculated location probability determined using thetree and a known set of anatomical element locations identified in atarget image. An example of a method for evaluating a set of decisiontrees to determine optimal trees is described further below with respectto FIG. 10.

At action 510, an image classifier is generated using the selectedoptimal trees. The selected optimal decision trees may be used toprocess pixels of a test image, and a probability value may be assignedto each pixel of the test image based on which leaf of each tree thepixel is assigned during the processing operation. An example of amethod for evaluating a test image using a decision tree is describedfurther below with respect to FIG. 11. It should be appreciated thatvarious elements of the method 500 may be repeated in order to generatea plurality of decision trees for use in the classifier. For example,different decision trees that correspond to different sets of Haar-likefeatures (e.g., different randomly generated sets) may be generated andevaluated for inclusion in the classifier.

Turning now to FIG. 6, an example set of 2-D Haar-like features aredescribed. As described above, Haar-like features may include a set oftwo or more rectangles for use in detecting objects within an image,with each rectangle representing a value such as −1 or 1. The Haar-likefeatures may be convolved or slid across an image to produce a newconvolved image. Given a simple rectangular Haar-like feature asdepicted in FIG. 6, a pixel in the convolved image may be defined as thedifference of the sum of pixels of areas inside each rectangle, whichcan be at any position and scale within the original image. This featureset is called 2-rectangle features. Haar-like features may also include3-rectangle features and 4-rectangle features. The values resulting fromapplication of a Haar-like feature to an image may indicate certaincharacteristics of a particular area of the image. Each feature type canindicate the existence (or absence) of certain characteristics in theimage, such as edges or changes in texture. For example, a 2-rectanglefeature can indicate where the border lies between a dark region and alight region.

FIG. 7 depicts an image sampling process 700 for generating an imageclassifier in accordance with some example embodiments. After generatingthe feature images as described above with respect to FIG. 5,embodiments may evaluate each feature image as compared to a known setof anatomical element locations provided in a target image. Thisevaluation may be performed by identifying pixel values at particularpixels of the target image and the corresponding pixel values in eachfeature image. A plurality of pixels may be selected from a target image702. These pixels may be selected at random, or they may be selected toobtain a certain sample distribution within the target image. Theseselected pixels may correspond to the same pixel location in each of thefeature images 704 generated by applying a Haar-like feature to a sourceimage. In this manner, the samples may line up such that if a pixel atcoordinates (100, 134) is sampled in the target image, the same pixel atcoordinates (100, 134) of each feature image may also be sampled. Thesesampled pixel values may be utilized to generate a decision tree and toevaluate the generated decision tree as described further below withrespect to FIGS. 8-10.

FIG. 8 depicts a flow chart illustrating an example of a method forgenerating a decision tree using a set of feature images. As describedabove, image features may be applied to a set of source images togenerate a set of feature images. Each source image may generate aplurality of feature images, with each feature image associated with oneof a set of features (e.g., the Haar-like features) as described above.This set of feature images may be evaluated together to generate adecision tree for use in evaluating other images. In particular, pixelvalues associated with particular pixel coordinates of each of the setof feature images may be utilized to build the decision tree.

At action 802, a feature is determined that creates an optimal split inany remaining elements of the tree, such as a set of pixel sample valuesassociated with the set of feature images. The optimal split may bebased upon characteristics of each pixel at a pixel sample locationwithin the feature image, and how those pixel characteristics relate tocharacteristics of pixels at the same location in the target image. Anexample embodiment for determining a feature that results in an optimalsplit is described further below with respect to FIG. 9.

At action 804, the tree is split using the feature determined at action804. Splitting of the tree may refer to placing pixels with pixel valuesthat are below a threshold defined for the feature on one leaf of anode, and pixels with pixel values that are greater than the thresholdon another leaf of the same node, thereby splitting the set of pixelsinto the two leaf nodes based on the threshold.

At action 806, the tree may be evaluated to determine if the tree iscomplete. For example, the tree may have a defined depth, and the treemay be considered complete when the defined depth has been reached.Additionally or alternatively, the tree may be considered complete whenno more pixels may be split (e.g., only one pixel remains at each leafnode). Embodiments may allow the use of the same feature at more thanone decision point in the tree, as the same feature may give the bestdiscrimination between more than one set of pixels, or a subset of thesame group of pixels. If the tree is not complete, the method may returnto action 802 to recursively evaluate the pixels of each leaf node todetermine an optimal feature for splitting the set of pixels in the newleaf node. Otherwise, the method proceeds to action 808.

At action 808, the pixel values of the target image corresponding to thepixels at each leaf node are evaluated to determine a probability to beassociated with that leaf. For example, the intensities of the targetimage pixels associated with the pixels of the particular leaf node maybe averaged, such that if an intensity of 0.1 indicates a 10%probability of the presence of an anatomical element, an intensity of0.5 indicates a 50% probability, and an intensity of 0.9 indicates a 90%probability, the probability assigned to a leaf node containing pixelscorresponding to target image pixels with the values of [0.25, 0.5,0.75, 0.9] would be 60%. This probability represents the probabilitythat a pixel that is assigned to that particular leaf during an imageclassification process contains an anatomical element. At action 810,the determined probability is assigned to the particular leaf. It shouldbe appreciated that the method 800 may be performed recursively to fillout the entire decision tree, including assigning a probability to eachleaf node of the tree. The tree may then be evaluated for accuracy asdescribed further below to FIG. 10.

Turning now to FIG. 9, an example of a method 900 for determining anoptimal feature for splitting a decision tree is described. As describedwith respect to FIG. 8, a decision tree may be generated by comparingpixel values associated with samples taken from a feature image withsamples taken from a target image to determine if the feature does anacceptable job of separating pixels that are related to anatomicalelements from pixels that are not related to anatomical elements. Themethod 900 describes a process by which particular features can beevaluated for accuracy and inclusion in a decision tree.

At action 902, a feature is selected for evaluation to determine howwell the feature splits a set of sample pixel values. As describedabove, the feature may be associated with a particular feature imagederived by applying a Haar-like feature to a particular source image.Each feature may also be associated with a particular set of pixelsample values derived from sampling of the feature image associated withthe feature. For example, if 11 pixel samples are taken, then eachfeature may be associated with an 11 value pixel vector corresponding tothe intensity of those particular pixels in the associated featureimage. As such, each feature image may be associated with a differentset of pixel values, owing to the different transforms performed on eachfeature image (e.g., different Haar-like feature used in convolution).

At action 904, a threshold is determined that splits the set of pixelsamples associated with the image into two bins. For example, thethreshold may be chosen such that an equal number of pixels have agreater intensity and a lesser intensity than the threshold, splittingthe set of pixels into two groups. It should be readily appreciated thatthe groups may not be equal. Since each feature may have a different setof associated pixel values, each feature may also have a separatethreshold used for separating the associated pixel values into twogroups.

At action 906, the values of the samples associated with the targetimage are determined for each group, and a variance is determined forthe set of target values. In other words, instead of using the pixelvalues for the feature image, the pixel values of the associated pixelsfrom the target image are used, since these values represent the actualknown location of anatomical elements. As such, the thresholddetermination step of action 904 is used to separate the pixels into twogroups using the values associated with the feature image, while thevariance of the pixel values of the separated groups is determined usingthe pixel values of the target image. In this manner, the validity ofsplitting based on the particular feature may be identified by comparingthe pixel group classification with known data from the target image,such that a low variance on each side of the split indicates a bettersplit, while a high variance indicates a sub-optimal split.

At action 908, the method determines whether any features are left to beevaluated for the set of pixels. If so, the method returns to action 902to determine a variance score for the next feature. Otherwise, themethod proceeds to action 910 to evaluate the features based on thedetermined variances.

At action 910, the feature that resulted in the split with the lowesttarget value variance is identified as the optimal feature for splittingthe set of sample pixels. It should be readily appreciated that themethod 900 may be repeated numerous times during creation of a decisiontree, in order to select a feature that results in an optimal split ateach node of the tree.

Turning now to FIG. 10, an example method 1000 is described forevaluating the accuracy of one or more decision trees and generating animage classifier based on the accuracy evaluation. As described above,embodiments may result in the generation of multiple decision trees.These decision trees may be evaluated against sample data from a knowntarget image or images to determine how close the predicted probabilityfor each decision tree is to known anatomical element location dataprovided in the target samples.

At action 1002, the method 1000 may begin by selecting a decision tree,such as one of the decision trees generated by the method 800 describedabove. At action 1004, a target image, in which the location of depictedanatomical elements is known a priori, may be applied to the decisiontree. For example, sample pixel values may be determined for particularpixel coordinates within the target image. These sample pixel values maybe evaluated using the decision tree, such that each pixel is assignedto a leaf of the decision tree (e.g., moving down the tree to a leafbased on where the pixel value falls in relation to a threshold). Inorder to evaluate each sample pixel using a particular feature,application of the target image to the decision tree may includegenerating a feature vector for each sample pixel, where the featurevector defines how the particular sample pixel would be modified if thetarget image were transformed using each particular feature. Evaluationof nodes in the tree may include using the term of the feature vectorcorresponding to the feature associated with the particular node. Inother words, the determination as to whether a particular pixel isgreater than or less than a particular feature threshold value may bedetermined using a pixel value resulting from a transform of the targetimage sample pixel with the particular Haar-like feature associated withthe particular evaluation node of the tree.

Once each of the sample pixels has been assigned to a leaf of the tree,at action 1006 a probability may be determined for each of the samplepixel values based on the leaf to which the value is assigned. Forexample, as described above with respect to FIG. 8, each of the leavesof the tree may be associated with a particular probability derived whenthe tree is constructed. At action 1008, a difference is determinedbetween the probability determined based on the classifier and knowndata associated with the sample. For example, if the leaf of thedecision tree indicates that a particular pixel has a 90% probability ofbeing associated with an anatomical element location, but the knownsample data indicates that there is no anatomical element at thelocation of the particular pixel, then the results provided by thedecision tree may be suspect. Similarly, if the decision tree indicatesa low probability that a particular pixel has an anatomical element, butthe known data indicates an anatomical element is located at that pixel,then this may indicate that the decision tree is suspect or otherwisenot providing quality results. Many such pixels may be evaluated foreach decision tree, as a certain number of “misses” or “false positives”may be expected, and decision trees may be evaluated based on anaggregate of results (e.g., an overall accuracy rate over 10, 50, 100,or 1000 pixel evaluations).

At action 1012, one or more trees with a minimum difference between theclassifier probability and known data (e.g., a highest accuracy rate)may be selected for inclusion in a classifier used to identifyanatomical element locations in test images. For example, fourclassifiers may be selected based on the four decision trees with thehighest accuracy.

Turning now to FIG. 11, an example embodiment is provided for applying aclassifier to a test image to assist with detection of anatomicalelements within the test image. As described above, a classifier mayinclude one or more decision trees generated using a set of trainingdata, as described above with respect to FIGS. 5-10. This classifier maybe applied to a test image to determine a probability that an anatomicalelement is located at each pixel of the image. These probabilities maybe used to generate a classified image, with pixel values of theclassified image each corresponding to a particular probability (e.g.,intensity or contrast values of each pixel associated with theprobability). This classified image may be used in conjunction with ananatomical model to identify one or more anatomical elements within thetest image.

At action 1102, a feature vector is generated for each pixel of the testimage. The feature vector may correspond to each feature associated witha particular classifier being applied to the test image to determine theimpact of the feature on a pixel value for each pixel of the image.Although the instant embodiment is described with respect to utilizingeach pixel of the image, it should be appreciated that certain subsetsof the pixels may also be employed according to various methods forselecting certain sets of pixels. For example, a reduced set of pixels(e.g., every other pixel) may be analyzed to reduce processor load.

At action 1104, the feature vectors are used to apply the classifier tothe test image. For example, if the classifier includes a set of fourdecision trees, each pixel vector may be fed through each tree todetermine to which leaf of the tree the pixel vectors is assigned. Theresulting four values (one value for each leaf of one of the fourclassification trees) may be combined (e.g., averaged) to determine anoutput value for each pixel. This process may be repeated by analyzingeach pixel vector using the one or more decision trees contained in theclassifier.

At action 1106, the pixel values for each pixel vector may be used togenerate a classified image. For example, each pixel value (e.g., anintensity of each pixel) of the classified image may correspond to theprobability that the particular pixel is associated with an anatomicalelement, as determined by the decision trees of the classifier. Thisclassified image may be provided to an anatomical model for evaluationto determine the location of anatomical elements within the originaltest image.

Example Method for Generating an Anatomical Model

Turning now to FIG. 12, an example embodiment for generating ananatomical model is described. As described above, an anatomical modelmay be generated for use in conjunction with an image classifier todetect the location of one or more anatomical elements in a test image.Generation of the anatomical model may be performed using pictorialimage evaluation techniques, where the location of particular anatomicalelements are derived from known data and a model is generated describingthe relationship between these anatomical elements. This model may beused to describe the size, shape, structure, form, location, and thelike of the anatomical elements.

At action 1202, a set of anatomical data may be received. As describedabove with respect to FIG. 4, the set of anatomical data may include aset of training images that are presented as a set of target images anda set of source images. In some additional or alternative embodiments,the anatomical model may also be generated using expert knowledge abouta particular anatomical structure (e.g., based on physiologicalstructure models developed by medical practitioners) to supplement orreplace the set of training images. However, the set of anatomical datamay additionally or alternatively not include image content. Forexample, instead of providing an image or set of images, the anatomicaldata may include raw data indicating various characteristics of knownanatomical data such as offsets, measurements, direction vectors betweenelements, or the like. As such, it should be readily appreciated that ananatomical model could be generated according to the embodimentsdescribed herein without reference to any image data, instead relyingupon non-image anatomical data.

At action 1204, a next set of anatomical data is selected forevaluation. For example, a next image of a set of image training datamay be selected, or a next row in an anatomical data table may beselected for evaluation. At action 1206, a set of anatomicalmeasurements are determined from the selected anatomical data. Forexample, the anatomical data may be evaluated to determine a set ofoffsets between two anatomical elements (e.g., between two adjacentvertebrae). Various other measurements may also be employed, such assize (e.g., width of veins and arteries), shape (e.g., shape of aparticular organ), and the like as described above. At action 1208, theanatomical measurements may be stored for later use in generation of ananatomical model.

At action 1210, a determination is made as to whether any anatomicaldata remains for evaluation. If so, the method returns to action 1204 toevaluate the next set of anatomical data, otherwise the method proceedsto action 1212 to proceed with generation of the anatomical model.

At action 1212, the method may fit the stored anatomical measurements toa model. For example, the method may fit a Gaussian to the anatomicalrelative offset measurements. The anatomical model may be generated forthe particular set of anatomical data based on the fit to the model. Theanatomical model may later be applied during an anatomical elementdetection process to determine a best fit of a set of probabilitiesrelated to a classified image. As described above with respect to FIG.4, anatomical elements may be identified based on minimizing an errorfrom the anatomical model while maximizing the probabilities determinedby the classified image.

It will be understood that each block of the flowcharts, andcombinations of blocks in the flowchart, may be implemented by variousmeans, such as hardware, firmware, processor, circuitry, and/or otherdevices associated with execution of software including one or morecomputer program instructions. For example, one or more of theprocedures described above may be embodied by computer programinstructions. In this regard, the computer program instructions whichembody the procedures described above may be stored by a memory 104 ofan apparatus employing an embodiment of the present invention andexecuted by a processor 102 of the apparatus. In some embodiments,portions of the various methods may be facilitated by a user instead of,in addition to, or in conjunction with an algorithm. For example, a usermay interactively choose features for a decision tree, decide whichtests are utilized at particular branches of a decision tree, decide aclass for a particular pixel, or the like.

As will be appreciated, any such computer program instructions may beloaded onto a computer or other programmable apparatus (e.g., hardware)to produce a machine, such that the resulting computer or otherprogrammable apparatus implements the functions specified in theflowchart blocks. These computer program instructions may also be storedin a computer-readable memory that may direct a computer or otherprogrammable apparatus to function in a particular manner, such that theinstructions stored in the computer-readable memory produce an articleof manufacture the execution of which implements the function specifiedin the flowchart blocks. The computer program instructions may also beloaded onto a computer or other programmable apparatus to cause a seriesof operations to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide operations for implementing the functions specified inthe flowchart blocks.

Accordingly, blocks of the flowchart support combinations of means forperforming the specified functions and combinations of operations forperforming the specified functions for performing the specifiedfunctions. It will also be understood that one or more blocks of theflowchart, and combinations of blocks in the flowchart, can beimplemented by special purpose hardware-based computer systems whichperform the specified functions, or combinations of special purposehardware and computer instructions.

In some embodiments, certain ones of the operations above may bemodified or further amplified. Furthermore, in some embodiments,additional optional operations may be included. Modifications,additions, or amplifications to the operations above may be performed inany order and in any combination.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments in the context of certain examplecombinations of elements and/or functions, it should be appreciated thatdifferent combinations of elements and/or functions may be provided byalternative embodiments without departing from the scope of the appendedclaims. In this regard, for example, different combinations of elementsand/or functions than those explicitly described above are alsocontemplated as may be set forth in some of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. A method for detecting anatomical elementscomprising: receiving a test image; generating a classified image byapplying an image classifier to the test image, the image classifiercomprising at least one decision tree for evaluating at least one pixelvalue of the test image and the classified image comprising a pluralityof pixel values, wherein each pixel value is associated with aprobability that an associated pixel is related to an anatomicalelement; and evaluating, using a processor, the classified image usingan anatomical model to detect at least one anatomical element within theclassified image.
 2. The method of claim 1, further comprising labelingthe detected at least one anatomical element within the test image inresponse to detecting the at least one anatomical element within theclassified image.
 3. The method of claim 2, wherein a location of theanatomical element within the test image corresponds to a location inwhich the anatomical element was detected within the classified image.4. The method of claim 1, further comprising generating the imageclassifier by: receiving a set of training images, the set of trainingimages comprising at least one target image and at least one sourceimage; determining at least one image feature; transforming the at leastone source image using the at least one image feature to generate atleast one feature image; generating at least one decision treecorresponding to the at least one image feature using at least the atleast one feature image and the at least one target image; and using thegenerated at least one decision tree as the image classifier.
 5. Themethod of claim 4, further comprising: generating a plurality ofdecision trees, each of the decision trees corresponding to a set ofimage features; evaluating the plurality of decision trees to determinean accuracy value for each decision tree; and selecting at least one ofthe plurality of decision trees with the highest accuracy value as theimage classifier.
 6. The method of claim 4, wherein the at least oneimage feature is a Haar-like feature.
 7. The method of claim 4, whereinthe at least one decision tree is generated by a process comprising:determining a set of pixel values associated with a particular node ofthe decision tree; determining a feature that results in a minimumvariance in target pixel values associated with the set of pixel values;and assigning the feature that results in a minimum variance in targetpixel values as a decision feature for the particular node of the tree.8. The method of claim 7, further comprising: determining a thresholdfeature value associated with the feature that results in the minimumvariance, wherein the threshold feature value results in a split in theset of pixel values when applied to the set of pixel values; andassigning the threshold feature value to the particular node of thedecision tree.
 9. The method of claim 1, further comprising generatingthe anatomical model by evaluating a set of anatomical data.
 10. Themethod of claim 1, wherein the anatomical model defines at least one ofa size of an anatomical element, a shape of an anatomical element, or anoffset between two or more anatomical elements.
 11. The method of claim1, wherein the anatomical elements are spinal vertebrae, and wherein theanatomical model defines an offset between adjacent vertebrae.
 12. Anapparatus comprising processing circuitry configured to: receive a testimage; generate a classified image by applying an image classifier tothe test image, the image classifier comprising at least one decisiontree for evaluating at least one pixel value of the test image and theclassified image comprising a plurality of pixel values, wherein eachpixel value is associated with a probability that an associated pixel isrelated to an anatomical element; and evaluate the classified imageusing an anatomical model to detect at least one anatomical elementwithin the classified image.
 13. The apparatus of claim 12, furtherconfigured to label the detected at least one anatomical element withinthe test image in response to detecting the at least one anatomicalelement within the classified image.
 14. The apparatus of claim 13,wherein a location of the anatomical element within the test imagecorresponds to a location in which the anatomical element was detectedwithin the classified image.
 15. The apparatus of claim 12, furtherconfigured to: receive a set of training images, the set of trainingimages comprising at least one target image and at least one sourceimage; determine at least one image feature; transform the at least onesource image using the at least one image feature to generate at leastone feature image; generate at least one decision tree corresponding tothe at least one image feature using at least the at least one featureimage and the at least one target image; and use the generated at leastone decision tree as the image classifier.
 16. The apparatus of claim15, further configured to: generate a plurality of decision trees, eachof the decision trees corresponding to a set of image features; evaluatethe plurality of decision trees to determine an accuracy value for eachdecision tree; and select at least one of the plurality of decisiontrees with the highest accuracy value as the image classifier.
 17. Theapparatus of claim 15, wherein apparatus is further configured to:determine a set of pixel values associated with a particular node of thedecision tree; determine a feature that results in a minimum variance intarget pixel values associated with the set of pixel values; and assignthe feature that results in a minimum variance in target pixel values asa decision feature for the particular node of the tree.
 18. Theapparatus of claim 17, further configured to: determine a thresholdfeature value associated with the feature that results in the minimumvariance, wherein the threshold feature value results in a split in theset of pixel values when applied to the set of pixel values; and assignthe threshold feature value to the particular node of the decision tree.19. The apparatus of claim 12, wherein the anatomical elements arespinal vertebrae, and wherein the anatomical model defines an offsetbetween adjacent vertebrae.
 20. A computer program product comprising atleast one non-transitory computer-readable storage medium bearingcomputer program instructions embodied therein for use with a computer,the computer program instructions comprising program instructionsconfigured to: receive a test image; generate a classified image byapplying an image classifier to the test image, the image classifiercomprising at least one decision tree for evaluating at least one pixelvalue of the test image and the classified image comprising a pluralityof pixel values, wherein each pixel value is associated with aprobability that an associated pixel is related to an anatomicalelement; and evaluate the classified image using an anatomical model todetect at least one anatomical element within the classified image.